Homebrew

Summarizing my attempts to understand Homebrew codebase

• https://github.com/Homebrew

• https://github.com/Homebrew/brew

• https://github.com/Homebrew/homebrew-core

• https://github.com/Homebrew/homebrew-cask

Terms:

• Formula - package definition.

• Keg - installation prefix of a formula.

• Cellar - where all kegs are located.

• Tap - git repo of formulae and/or commands.

• Bottle - pre-built keg.

• Cask - extension of Homebrew to install native MacOS apps.

General notes:

• I like how formulae come with tests.

• Formula dev guide is pretty great.

• Ruby seems like a great choice for DLSs like this.

• Overall code structure seems moderately simple, e.g. there are not too many layers of redirection for the most part.

• Implementation details are often rather convoluted, with not too many comments.

• A lot of long methods.

Tracing:

• Entry point shell script: https://github.com/Homebrew/brew/blob/master/bin/brew
• Then https://github.com/Homebrew/brew/blob/master/Library/Homebrew/brew.sh

  • Setting env variables for OS, cache location, etc.

  • Checks that it's not sudo, not installing on temp, etc.

  • Check dependencies: curl, git, ...

  • Then route to one of https://github.com/Homebrew/brew/tree/master/Library/Homebrew/cmd

    • Some are .sh, some are .rb

    • I expected a single ruby entry point, but there's none!

• Install path:

  • https://github.com/Homebrew/brew/blob/master/Library/Homebrew/cmd/install.rb

    • Test: https://github.com/Homebrew/brew/blob/master/Library/Homebrew/test/cmd/install_spec.rb Seems rather... superficial. But I kind of like their test DSL.
  • Command parser: https://github.com/Homebrew/brew/blob/master/Library/Homebrew/cli/parser.rb
  • Check if to install: https://github.com/Homebrew/brew/blob/aa14e48f4e73d2f4c7d178d7b8a2f528b74995d7/Library/Homebrew/install.rb#L95
  • Install: https://github.com/Homebrew/brew/blob/aa14e48f4e73d2f4c7d178d7b8a2f528b74995d7/Library/Homebrew/install.rb#L232

    • Accepts formula and a ton of params.

    • I would probably extract the params into some class.

  • Then it creates FormulaInstaller and calls its methods one by one: prelude, fetch, install, finish.
  • FormulaInstaller seems... rather convoluted.

Interesting:

• Did you mean? https://github.com/Homebrew/brew/pull/11565/files

  • Not too interesting. It just delegates.

• Locking. https://github.com/Homebrew/brew/blob/master/Library/Homebrew/lock_file.rb
• Github access https://github.com/Homebrew/brew/blob/aa14e48f4e73d2f4c7d178d7b8a2f528b74995d7/Library/Homebrew/utils/github.rb With pagination and what not. Spec: https://github.com/Homebrew/brew/blob/master/Library/Homebrew/test/utils/github_spec.rb
• Search: https://github.com/Homebrew/brew/blob/master/Library/Homebrew/search.rb
• Download strategy switch: https://github.com/Homebrew/brew/blob/09f7bc27a99469cf947431df4754737dfbadb31d/Library/Homebrew/download_strategy.rb#L1323-L1356
• Unpack strategy. https://github.com/Homebrew/brew/blob/master/Library/Homebrew/unpack_strategy.rb https://github.com/Homebrew/brew/tree/master/Library/Homebrew/unpack_strategy
• Cache store: https://github.com/Homebrew/brew/blob/master/Library/Homebrew/cache_store.rb
• Curl & workarounds: https://github.com/Homebrew/brew/blob/04532cb6216b69a5b067aa7a4e22cff0944b257d/Library/Homebrew/utils/curl.rb#L64